Electroless Nickel Boron Coatings Research Articles

The effect of reduced graphene oxide concentration on the wear behaviour of reduced graphene oxide–nickel–boron (Ni–B–rGO) electroless coatings

In this article, the electroless nickel-boron coatings containing different rGO concentrations (0,6, 20.5, 35 and 40 mg/L) were deposited on AISI 4140 steel. Their structural properties were examined using X-ray diffraction, Raman spectroscopy, infrared spectroscopy, scanning electron microscopy and hardness analysis. Moreover, their friction coefficient and wear properties were studied using a pin-on-disc test. The results showed that as the rGO concentration increased, the structure of the coating changed from amorphous to semi-crystalline. Adding rGO up to 20.5 mg/L increased the hardness of the as-plated NiB coating from 519 to 863 Hv and reduced its specific wear rate from 1.28 × 10−9 to 0.68 × 10−9 kg/Nm. However, increasing the rGO concentration to 40 mg/L led to rGO agglomeration and increased the specific wear rate of the coating.

Tribological Behaviors of Electroless Nickel-Boron Coating on Titanium Alloy Surface

Titanium alloys are excellent structural materials in engineering fields, but their poor tribological properties limit their further applications. Electroless plating is an effective method to enhance the tribological performance of alloys, but it is difficult to efficiently apply to titanium alloys, due to titanium alloy’s strong chemical activity. In this work, the electroless Nickel-Boron (Ni-B) coating was successfully deposited on the surface of titanium alloy (Ti-6AL-4V) via a new pre-treatment process. Then, linearly reciprocating sliding wear tests were performed to evaluate the tribological behaviors of titanium alloy and its electroless Ni-B coatings. It was found that the Ni-B coatings can decrease the wear rate of the titanium alloy from 19.89×10−3 mm3 to 0.41×10−3 mm3, which attributes to the much higher hardness of Ni-B coatings. After heat treatment, the hardness of Ni-B coating further increases corresponding to coating crystallization and hard phase formation. However, heat treatment does not improve the tribological performance of Ni-B coating, due to the fact that higher brittleness and more severe oxidative wear exacerbate the damage of heat-treated coatings. Furthermore, the Ni-B coatings heat-treated both in air and nitrogen almost present the same tribological performance. The finding of this work on electroless coating would further extend the practical applications of titanium alloys in the engineering fields.

Tribological behavior of electroless Ni-B ternary and quaternary coatings with inclusion of W and Mo

Electroless nickel coatings help to tailor requisite surface properties in materials for use in various applications. The aim of the present study is to examine the tribological behavior of electroless nickel-boron coatings incorporated with Mo and W. The coated layers are developed over pin samples with various bath compositions. The coated specimens are characterised to assess their basic features. The tribological tests are carried out with the help of a pin-on-disc tribo-tester under dry conditions. The coating characteristics are determined to comprehend the importance of tungsten as well as molybdenum concentration in electroless nickel-boron coatings. In the as-deposited state, all the coated specimens displayed a surface morphology resembling cauliflower. Moreover, the roughness of these coated surfaces in their as-deposited state showed an increase corresponding to the concentration of the bath parameter, resulting in a higher coefficient of friction (COF). The addition of Mo into Ni-B matrix promotes the coarse grained and cracked surface morphology leading to highest friction coefficient value of as-deposited Ni-B-Mo coatings. The highest surface roughness of Ni-B-Mo coatings also leads to the highest specific wear rate due to breaking and crushing of roughness peaks. The present study reveals the effect of incorporation of W and Mo in electroless Ni-B coatings to control the friction and wear characteristics of the specimens. This will help in deciding the proper electroless bath compositions for specific tribological applications.

Replacing Toxic Hard Chrome Coatings: Exploring the Tribocorrosion Behaviour of Electroless Nickel-Boron Coatings

Electroless nickel-boron coatings present outstanding properties such as high hardness, excellent wear resistance and uniform coating, and thus they are considered to be alternative to toxic hard chrome coatings. However, they contain lead that is toxic and used as stabilizer in the plating bath. This study aims to investigate the tribocorrosion behaviour of lead-free electroless nickel-boron coatings. In the present research, several tests were carried out to investigate the behaviour of these coatings under both dry and tribocorrosion reciprocating sliding wear against alumina balls, at room temperature. The open circuit potential (OCP) method was used to determine the degradation mechanism of the coatings. The results of the tribocorrosion and dry wear tests showed that the performance of coatings was very different from each other. A steady state for the coefficient of friction (COF) is achieved during the tribocorrosion test, whereas the constant production of debris and their presence in the contact implied an increase in COF with distance during the dry wear test. The wear mechanisms of these coatings also presented variations in these tests. It was found that the wear area calculated from tribocorrosion is lower (56 µm2) than the one from dry sliding test (86 µm2).

Investigation of Ni-Cu-B and Ni-Cu-Sn-B coatings developed by electroless method

Due to their remarkable mechanical properties and tribological behaviour which is equivalent the hard chrome coating, electroless Nickel–Boron coatings have been employed in a variety of industries. With the advent of emerging and challenging applications, there has been a need to develop newer variants of the novel Ni-B binary variant. The present work therefore investigates Ni-B-Cu coatings in a quest to achieve higher wear and corrosion resistance. A stabilizer free bath and tin chloride stabilized bath was formulated for the same to remove the harmful lead nitrate from the coating formulation. The concentration of copper sulphate was varied from 0.3 to 0.7 g/L in both the bath formulations. Based on the mass gain of the specimens, coatings obtained from 0.6 g/L copper sulphate was further investigated. The surface morphology of as-plated samples was observed which shows nodular structure and the growth was different compared to lead stabilized baths. The constant load and progressive scratch test were done to evaluate scratch hardness and coating failure respectively.

Deposition and process parameter optimization of electroless Ni-B coating from a stabilizer free bath to achieve enhanced microhardness, scratch-hardness and adhesion using taguchi’s methodology

Electroless nickel boron coatings have wide industrial usage. However, they are generally obtained from a lead-stabilized bath. The present work investigates and optimizes the scratch-hardness and microhardness obtained from stabilizer-free electroless nickel boron bath in a quest to eliminate lead nitrate/heavy metals, which are potentially toxic. The bath temperature, heat treatment temperature, and duration were varied at three levels. Enhanced scratch-hardness (12.581 GPa) was obtained at 85 °C bath temperature and heat treatment at 350 °C for 1 h. At the same time, the highest microhardness (886.17 HV100) was obtained at a parametric combination of 95 °C bath temperature and heat treatment at 450 °C for 1 h. Multi-objective optimization was carried out using grey relational analysis. The parametric combination predicted in multi-objective optimization was 85 °C bath temperature and heat treatment at 350 °C for 1 h where the microhardness was 846.34 HV100. Furthermore, an analysis of variance was also carried out to investigate the importance of the factors in controlling scratch-hardness and microhardness. The highest contribution was observed from heat treatment duration. Further investigation of the optimized coating was done by the progressive scratch test, which recorded that the first critical load of failure improved compared to non-heat treated electroless Ni-B coatings. The coatings were also characterized using field emission scanning electron microscope, energy dispersive x-ray spectroscopy, and x-ray diffraction. The coatings in optimized condition showed no transverse or chevron cracks within 5–24 N.

Modelling and Optimization of Amphoteric Surfactant Concentration in Electroless Nickel Boron Coatings for Maximum Microhardness

In the electroless nickel-boron coating process, surfactant helps to minimize the surface tension between the substrate and the electrolyte in the bath. Despite, its high cost and the formation of micelles from monomeric surfactant molecules at its critical micelle concentration (CMC), it is essential to optimize the concentration while using in the bath. In this study, to solve this problem, mathematical models are developed using regression and artificial neural network (ANN) techniques to relate the concentration of amphoteric surfactant (0-0.162 g/L) as an independent variable and microhardness as a dependent variable. Then, the developed model was used to optimize microhardness at CMC using a genetic algorithm (GA). The goodness of fit of the models was evaluated using the coefficient of determination (R2). The ANN model was found to be the best fit with R2 = 0.99. The maximum microhardness of 852 HV was achieved at the CMC of 0.064 g/L, from the GA using the validated model as a fitness function.

Selection of New Heat Treatment Conditions for Novel Electroless Nickel-Boron Deposits and Characterization of Heat-Treated Coatings

Electroless nickel-boron coatings were deposited from a novel deposition bath that was stabilizer-free. Those coatings were analyzed by DSC to determine the crystallization temperature of nickel-boride phases, and then the best heat treatment conditions for the new coatings were selected using the Knoop hardness test and XRD. The results of DSC analysis and XRD were coherent with the findings of previous studies, which shows that the new coating has a boron content lower than 4% wt. The maximum hardness was obtained after heat treatment at 300 °C for 4 h and reached 1196 ± 120 hk50, which is much higher than the as-deposited coating. The heat-treated coatings were then fully characterized using optical and scanning electron microscopy, as well tribological and corrosion tests. Various sliding tests (ball-on-disk and ball-on-flat configurations) were conducted to analyze the coefficient of friction (COF) and wear behavior of the coatings. The maximum von Mises stress was calculated, and values of 624 MPa and 728 MPa were obtained for the ball-on-disk and ball-on flat, respectively, at a depth close to 14 µm from the surface, confirming the suitability of the applied load. Abrasive, adhesive, and fatigue wear mechanisms were observed on the worn sample morphology using SEM. It has been determined that during the corrosion test the OCP and corrosion potential values for the heat-treated coating increase as compared with the as-deposited one, whereas its corrosion resistance decreases.

Effect of Morphological and Microstructural Variations on the Properties of Electroless Nickel Boron Coatings

Effect of Morphological and Microstructural Variations on the Properties of Electroless Nickel Boron Coatings

Process Modeling and Intuitive Search Based Optimization of Average Surface Roughness in Citrate Stabilized Electroless Nickel-Boron Coatings

Process Modeling and Intuitive Search Based Optimization of Average Surface Roughness in Citrate Stabilized Electroless Nickel-Boron Coatings

Recent advances in electroless nickel‑boron coatings

Electroless nickel‑boron coatings have been used in various industrial sectors for more than 40 years due to their excellent mechanical and tribological properties, that exceed those of hard chrome, with homogeneous surface finishing, and competitive corrosion resistance. Standard electroless nickel‑boron coatings are usually confined to use in niche applications such as saw blades, firearms, and valves in the oil and gas industry due to the presence of heavy metals from the stabilizing agent in the coated system. However, recent advances in technology have made it possible to remove heavy metals but also to improve the productivity and properties of the coatings, sometimes in a remarkable manner. This introduces the standard EN-B coatings and their properties and highlights the most recent improvements, variants in bath composition and process and applications of electroless nickel‑boron; such as the production of lead and thallium-free coatings, the effect of ultrasonics and surfactants, composite and multi-alloy coatings, but also innovative post-treatments to provide a wide panorama of the recent advances in the field. Finally, the review brings light to the new developments that are still necessary in the field to narrow the gap between research and industrial development and enlarge the niche area of utilization. • EN-B coatings present high hardness, making them excellent candidates for the replacement of hard chrome. • Removing heavy metal stabilizer from electroless nickel-boron opens new fields of applications such as automotive. • Use of ultrasound allows increasing the plating speed of electroless nickel-boron without losing in properties. • Properties of electroless nickel-boron coatings can be tuned by using composite, multilayers, and alloy coatings. • Bath replenishment and recycling are still limited, developing methods for sustaining plating bath life is required.

Artificial neural network modelling for average surface roughness in citrate stabilised electroless nickel boron coatings

In this study, electroless nickel boron coatings were developed on Al 7075 aluminium alloy from the citrate stabilised electrolyte bath to investigate the applicability of artificial neural network (ANN) in the prediction of the average surface roughness Ra of the coatings. The process parameters such as concentrations of nickel, reducing agent and stabiliser were considered as input parameters and Ra was selected as an output parameter. Two different feed forward back propagation neural network architectures 3-10-1 and 3-5-5-1, were constructed and trained using Levenberg-Marquardt (LM) algorithm to predict the Ra. The accuracy of the networks was compared with the predicted coefficient of determination (R2) and mean squared error (MSE). The R2 and MSE of 0.9998 and 6.32E-05 were obtained for 3-5-5-1 against 0.9850 and 6.29 E-04 for 3-10-1 network architecture, which proved that the multi-layer perceptron (3-5-5-1) fits well for the experimental data presented.

Modelling and optimisation of hardness in citrate stabilised electroless nickel boron (ENi-B) coatings using back propagation neural network – Box Behnken design and simulated annealing – genetic algorithm

ABSTRACT In this work, a novel citrate stabilised electroless bath was developed and the process parameters (concentrations of nickel, reducing agent, and stabiliser) were optimised to achieve the maximum hardness in the ENi-B deposit on 7075-T6 aluminium alloy, using the back-propagation neural network (BPNN), Box–Behnken design (BBD), simulated annealing (SA) and genetic algorithm (GA). The effect of independent variables on dependent variable was modelled using the BPNN and BBD. The models were assessed for their significance using the coefficient of determination (R2) and mean squared error (MSE). The MSE and R2 of 34.18 and 0.9852 were obtained for BPNN model against 20.48 and 0.9911 for BBD, which proved that the BBD fits well to the experimental data. The optimum nickel ion, reducing agent and stabiliser concentrations of 29.86, 0.77 and 30.92 g L−1 were obtained from BBD for the maximum hardness of 592 HV. The local optimum values obtained from BBD were compared with global optimisation techniques, SA and GA, and the values were validated through experiments carried out in triplicate. The maximum hardness from local and global optimisation techniques was identical, with negligible change in the values of optimised process parameters. X-ray diffraction and scanning electron microscopy methods were used to examine the elemental composition and surface morphology, respectively, before and after heat treatment.

Effect of plasma nitriding temperature on microstructure and wear properties of electroless nickel-boron coatings

This study investigates the effects of plasma nitriding (PN) temperature on the microstructural properties and wear behavior of electroless nickel‑boron (ENB) coatings. To this end, the ENB coatings are deposited on the mild steel substrates and submitted to PN treatment at 350, 400, and 450 °C. The Morphology, roughness, microstructure, microhardness and wear resistance of the coatings are evaluated and compared to the conventional heat-treated ENB coatings. The results indicate that a crystalline structure has appeared in the as-deposited amorphous ENB coatings through PN treatment, leading to enhancement of their hardness. The highest hardness value (1406 HV0.1) and consequently the highest wear resistance are obtained for the PN-treated ENB coating at 350 °C. These results could be assigned to the grain growth suppression achieved by doping nitrogen atoms into the coating through PN treatment. Moreover, the precipitation of the lubricant h-BN phase during PN treatment of the ENB coatings has decreases the coefficient of friction in the sliding wear test.

Effect of borohydride concentration on tribological and mechanical behavior of electroless Ni-B coatings

Electroless Nickel boron (Ni-B) coatings were deposited over mild steel substrates to study the effect of borohydride concentration on tribological behaviour and mechanical properties. Three different types of coating bath solutions were used to deposit coatings. The as-deposited coatings were characterised based on surface morphology, composition and phase structure using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD), respectively. Friction and wear behaviour of the as-deposited coatings were evaluated by pin-on-disc tribo-tester. Coefficient of friction of the coatings decreases with the increase in borohydride concentration. Surface hardness, elastic modulus and scratch resistance behaviour of the coatings were evaluated using the data obtained by nano-indentation techniques. It is seen that the surface hardness and elastic modulus of the as-deposited coatings increase with the increase in borohydride concentrations. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarisation tests were conducted to analyse corrosion behaviour of the coatings against a corrosive environment of 3.5% NaCl solution. The corrosion test results displayed an increasing trend of corrosion resistance as the borohydride concentration increases in the coating bath solution.

Effect of temperature on ultrasound-assisted electroless nickel-boron plating

Electroless nickel-boron coatings have several advantages over electroplated nickel and electroless nickel-phosphorous: they are harder than both other coatings and, as all electroless coatings, can be applied easily to complex shapes and all substrates, even non conducting ones, contrary to electroplated coatings. Preliminary testing has proved that ultrasound assistance helps improve their properties by increasing the plating rate while conserving the properties of the coating.In this study, the effect of plating temperature on mechanically agitated and ultrasonic assisted electroless nickel-boron deposition was investigated: deposition was performed in two different configurations: one with a classical mechanical agitation at 300 rpm and the other employing ultrasound at a frequency of 35 kHz. In addition, different temperatures in the 80–95 °C range were tested. The increase of plating rate previously observed was confirmed and it was possible to lower slightly plating temperature while conserving plating efficiency, which decreases evaporation of the solution. Morphological, mechanical, corrosion and wear characterization were performed on the coatings, as well as tribocorrosion studies in an alkaline environment (0.1 M NaCl). Ultrasound-assisted coatings presented tribocorrosion behaviour that was similar or better than the standard ones.

The tin stabilization effect on the microstructure, corrosion and wear resistance of electroless NiB coatings

The effect of tin chloride on bath stabilization and properties of electroless Nickel-Boron (NiB) coatings was investigated. NiB coatings were synthesized by electroless deposition using SnCl2 stabilizer. Sn was codeposited in the coating generating a novel NiB-Sn alloy. The deposition of NiB-Sn occurred in an aqueous bath containing a reducible metal salt (NiCl2), reducing agent (NaBH4) and complexing agent (C2H4(NH2)2). The pH was controlled at pH 12 ± 1 in order to avoid bath destabilization. The stabilizer properties of SnCl2 were proved by the fact that the plating completely stops at high concentrations. It has been found in the present work that the SnCl2 not only stabilizes electroless nickel baths but also enhances the plating rate. The deposition was performed with three different concentrations of SnCl2 (0.05 g/L, 0.1 g/L and 0.2 g/L). The morphological features are modified as a function of concentration. Coatings with finer cauliflower structure and more homogeneous thickness are reached with the increase of stabilizer concentration. The corrosion behavior was increased with the Sn presence in the surface. Results for samples with 0.1 g/L of SnCl2 show hardness (842 hk50) wear behavior (Ws 0.11 μm2/N) and first damage by scratch test (Lc 30 N) results comparable to those presented by traditional NiB coatings.

Optimization of electroless NiB deposition without stabilizer, based on surface roughness and plating rate

The study of the roughness and plating rate of electroless nickel-boron (NiB) coatings produced without stabilizer and the optimization of bath composition based through an experimental design are herein presented. Experiments were carried out using different combinations of a complexing agent, ethylenediamine, and a pH regulator, sodium hydroxide, used in different concentrations. Sodium hydroxide addition showed to improve the plating rate while the incorporation of ethylenediamine affected the roughness of the film in the studied intervals. The optimum combination of bath composition for minimum roughness with maximum deposition rate was derived from the analysis. In order to obtain a film with a thickness between 10.0 and 10.7 μm and a roughness (Ra) between 0.22 and 0.25 μm, both reagents should be combined in the following concentrations: 120.0 < Ethylenediamine (g.L−1) < 128.7 and 151.7 < NaOH (g.L−1) < 160.0. The surface and cross-section morphology of the resulting coatings did not present the typical cauliflower-like structure of electroless nickel-boron due to a different mode of growth. The NiB coatings obtained in this study present 8 wt%. Boron in the composition and a surface hardness of 719 hv20. High corrosion resistance is observed after 240 h of neutral salt spray test.

Mechanical and wear characterization of electroless nickel mono and bilayers and high boron-mid phosphorus electroless nickel duplex coatings

Abstract The mechanical and wear properties of electroless nickel monolayer, bilayers and duplex NiP/NiB coatings were investigated in the as deposited state. Bilayers and duplex coatings, constituted of two layer of 10 μm each, were prepared according to four distinct configurations (NiB/NiP; NiP/NiB; NiB/NiB and NiP/NiP). Single layer coatings from each electroless nickel bath with a thickness of 20 μm were also synthesized and analyzed in this work: mid phosphorous NiP (nickel-phosphorus) and high boron NiB (nickel-boron). The microhardness, roughness and wear resistance of electroless nickel duplex coatings were compared with electroless NiP and NiB coatings of similar thickness. The hardness characteristics of duplex coatings are really influenced by the high hardness of NiB coatings: the hardness of pure NiP coatings was 550 HV while the presence of NiB coating as underlayer allowed to reach 738 HV. SEM observations of the cross-sections of the nickel duplex coatings also reveal that coatings are uniform with proper compatibility between layers.

Influence of Surfactants on the properties of electroless nickel boron (thallium and lead-free) coatings

Electroless nickel boron coatings were prepared from thallium and lead-free alkaline bath. The influence of surfactants on the properties of electroless nickel boron coatings was studied. Three surfactants namely sodium dodecyl sulfate, cetyltrimethyl ammonium bromide and 3-(N, N–Dimethylmyristylammonio) propanesulfonate were used. Morphology, microhardness, surface finish, topography and corrosion resistance of the coatings were evaluated. Electroless nickel boron coatings with addition of surfactant sodium dodecyl sulfate, cetyltrimethyl ammonium bromide and 3-(N, N-Dimethylmyristylammonio) propanesulfonate results in a smooth surface, with an average roughness value (Ra) of 0.220 µm for cetyltrimethyl ammonium bromide, 0.198 µm for sodium dodecyl sulfate and 0.174 µm for 3-(N, N-Dimethylmyristylammonio) propanesulfonate which are less than the Ra without surfactant addition (0.256 µm). The deposits had a microhardness value of 590 and 743 HV in the as-plated and heat-treated conditions, respectively. With addition of sodium dodecyl sulfate, cetyltrimethyl ammonium bromide and 3-(N, N-Dimethylmyristylammonio) propanesulfonate, a significant improvement in the microhardness is observed. Potentiodynamic polarization tests were carried out in 3.5 wt% NaCl to determine the real anticorrosion performance of the electroless nickel boron deposits. The entire experimental procedure, the results achieved, and their investigation are presented in this paper.